The present invention relates to a method for, and an apparatus therefor, indicating load condition of a cargo on a fork of a forklift truck.
When the cargo loaded on the fork exceeds a predetermined load limit, there appears a danger of forward overturning of the forklift through lifting up of rear wheels. For the purpose of preventing this danger various apparatuses or devices have been traditionally proposed. A few of representatives among them are introduced hereunder.
(1) A load condition indicating apparatus, disclosed in the publication laid open in JITSU-KAI-SHO 54(1979)-15887 (Japanese utility model application), wherein the weight of the cargo on the fork is indicated through detection of hydraulic pressure in the lift cylinder.
(2) An overload prevention apparatus, disclosed in the publication laid open in TOKU-KAI-SHO 54(1979)-49752 (Japanese patent applicaton), wherein overloading of the cargo is prevented through the action of a hydraulic pressure cutoff valve due to an output signal from a pressure switch for detecting the hydraulic pressure of the tilt cylinder, which is set in advance at a pressure corresponding to an allowable limit of forward turning moment of a forklift truck.
The apparatus disclosed in the above (1) is incapable of accurately warning the overturn danger, because it attempts to make a judgement of the danger only by the magnitude of the weight of the cargo, neglecting a fact that the forward turning moment of the forklift truck is largely influenced by the position of the cargo where it is placed on the fork. The apparatus disclosed in the above (2) is not free from some complaints, either, because the same, which attempts to make a judgement of danger only based on the magnitude of the forward turning moment, is insufficient for rightly indicating whether the cargo is ready so heavy as to risk an overturn or whether the danger may be avoided by changing the place of the cargo laid on the fork. If the difference between an overturn risky weight and an actual weight of the cargo in response to each placed position of the cargo on the fork is appreciable to a truck operator, operation efficiency of cargo work can be elevated a great deal, which enables the forklift trucks to be used at the highest possible capacity.